Machine tool feeding means



Sept. 4, 1934. E HELLER 1,972,560

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Patented Sept. 4, 1934 v UNITED sTA TEs PATENT OFFICE 1,922,580 MAcHmE Toor. FEEnmG MEANS Ernst Heller, Nurtingen, Germany Application November 19, 1932, Serial No. 643,327

In Germany November 26, 1931 3Claims.

My invention relates to machine tools and more particularly to their feeding means andthe regulation of the feed.

It is an object of my invention to improve a 5 machine tool having a fluid-controlled mechanism for feeding and returning a tool with respect to a work piece. To this end I provide a principal pump for supplying fluid under pires-A sure to the Huid-controlled mechanism, and with this principal pump I combine a feed pump.` 'Ihe feed pump is adapted to be regulated and is, at

, its suction side, connected to the principal pump 'Ihe solution mostly adopted is to provide a hyn draulic cylinder and to throttle the discharge of piston which is opposite the side on which the fluid acts for feeding the tool. However, it hasy been found that the regulation effected by such the fluid from the cylinder at that side of the throttling is subject to variations so that it is. necessary to frequently readjust the throttling means. The principal cause of the variation is the thinning of the uid, usually oil, with increasing temperature. The temperature of the oil rises during the operation of the machine so that the amount of oil flowing through the throttle valve which has been adjusted for oil of normal viscosity, is steadily increased and the feed movement becomes too great.

Another drawback of the aforesaid throttling means is that the pressure gradient at the throttle valve decreases with increasing resistance to the feed, so that the feed movement becomes too small with increasing resistance.

It has already been suggested to eliminate the influence of viscosity by providing means such as a metering pump for regulating the discharge of the fluid. The drawback 'of this solution is thatthe back pressure on the piston is high and that, consequently, .the pressure exerted on the opposite side of the piston for feeding it, must be higher still, i. e. the load on the feed pump is very high. The high back pressure also acts unfavorably on the metering pump whose pistons or valves are worn to such an extent that they require exchanging several times per year. The load on the metering pump is highest for the short feeds with which machine tools are normally operated so that the metering pump is worn most under normal operating conditions, resulting in unequal feed. Apart from this, the

energy consumen in the'f'eed pump is altogether gutdof proportion tothe power demand of the Another drawback of the metering system is that the back pressure decreases with increasing resistance to the feed. If the resistance is equal vto the force exerted in the hydraulic cylinder, the back pressure becomes nil, the metering pump becomes inactive and the regulation of the feed becomes inaccurate.

'I'hese drawbacks are eliminated according to my invention by providing, in combination with a principal pump for supplying the fluid under pressure, a feed pump which is adapted to be regulated. By these means the influence of temperature is absolutely eliminated andthe reduction of the feed with increasing resistance can be avoided altogether, or limited to any desired amount.

The feed pump can be entirely relieved of load so thatsit serves only as a meter for the exact regulation of the feed but not for transmitting forces. Its wear, therefore, isI practically nil and in any case is Without influence on the amount of feed for which the machine has been reguated.

If the power demand for the feed is small the principal pumpoperates at low delivery pressures, and generally the power demand of the principal pump varies with the increase or decrease of the feeding resistance.

-In the drawing amxed to this specification and forming part thereof a feed-regulating system embodying my invention is illustrated diagrammatically by way of example as' adapted to a cold saw.

Referring now to the drawing, 1 is a work piece, here shown as a round iron bar, 2 is the support for the work piece, and 3 is a hydraulic chuck for holding the work piece on the support, a hydraulic cylinder 4 with a supply pipe 5 being provided for exerting pressure on the chuck 3.

6 is a cold saw, 7 is a carriage in which the shaft 8 of' the saw is mounted to rotate, and 9 indicates a portion of a frame on which the carriage '1 is mounted toslide. The means for rotating the cold saw 6 may be of any suitable kind and have not been illustrated. 10 is a cylinder which is secured to the frame of the machine by any suitable means (not shown), 11 is a piston in the cylinder, 12 is the piston rod, and 13 is a lug on the carriage '7 to which the piston rod 12 is secured at its outer end. The piston 11 subdivides the cylinder into a front compartment 15 and a rear compartment 14.

16 is a reservoir for the fluid by which the piston 11 in the cylinder 10 is controlled, the fluid in the present instance being oil, 17 is the principal pump which is actuated by any suitable means such as a belt 18, 19 is the suction pipe of the principal pump and 20 is a strainer at the lower end of the suction pipe 19 for retaining foreign matter. principal pump which is the suction pipe' of the feed pump 22, 23 is a belt for actuating the feed pump 22, and 24 is a lever for regulating the delivery of the feed pump and for reversing it, the lever having a forward or feeding position I, a neutral position II and a return position III. By suitably adjusting the lever 24, the delivery of the pump is regulated. Regulating means of this kind are old in the art and will not be described.

i 25 is the delivery pipe of the feed pump 22 which vmi is connected to the front compartment 15 of the cylinder 10, and 26 is a pipe by which the delivery pipe 21 of the principal pump 17 is connected to the rear compartment 14 of the cylin der 10, by-passing the feed pump 22.

27 is a pipe which connects the delivery and suction pipe 21 to a valve casing 28, 29'is la tubu` lar valve, with holes 30 in its skirt and a valve body 31 on a seat in a chamber 32 of the casing 28. 34 is a hollow plug which is screwed into the casing at the open end of the chamber 32. 35 is a plunger which is mounted toslide in the cavity of the plug 34, 36 is a flange on the inner end of the plunger 35 which bears on the inner faceof the plug 34, and 37 is a spring in the chamber 32 one end of which bears on the valve body 31 while its other end bears on the flange 36 of the plunger 35. The spring 37 tends yto apply the valve body 31 to its /seat in the casing 28 and the fiange 36 of the plunger 35 to the inner face of the plug 34. The initial tension of the spring is varied by turning the plug 34. 38 is a pipe by which the cavity of the plug 34 is connected to the delivery pipe 25 of the feed pump 22 so that the plunger 35 is under the pressure of the iiuid in the pipe 25, and 39 is a return pipe by which the chamber 32 in the casing 28 is connected to the reservoir 16. 40 is a pipe by which the chamber A32 is connected to the tubular casing 41 of a safety valve 42 which is loaded by'a spring 43. The seat of the safety valve 42 is connected to the delivery pipe 25 of the feed pump by a pipe 43. l

44 is a pipe extending fromthe pipe 40 to the casing 45 of a rotary valve 46 which is operatively connected to the lever 24 of the feed pump 22 by a link 47 and a lever 48; 49 is a bore in the valve 46 which is so positioned with respect to thelever 48 that it registers with the opening of the pipe 44 when the lever 24 is in its reversing position III. 50 is a pipe which connects the delivery pipe 25 of the feed pump 22 to the casing 45 of the rotary valve 46, its opening being diametrally opposite the opening of the pipe 44.

The operation of my feed-regulating system is as follows:-

At the beginning of the operation the parts are in the positions illustrated. When the principal pump.19 and the feed pump 22 are started, the principal pump draws oil from the reservoir 16 and delivers it to the suction side of the feed pump 22 through pipe 21, and to the rear compartment 14 of the cylinder 10 through pipe 26. The feed pump 22 which has been regulated for a given delivery by adjusting its lever 24the lever being shown in the position I corresponding to maximum delivery-forces the liquid which 1S Supplied 21 is the delivery pipe of they to it by the principal pump 17, into the compartment 15 of the cylinder 10 through pipe 25. The piston rod 12 is comparatively thick and therefore the area of the piston 11 which is exposed to the back pressure from pipe 26, is smaller than for instance one half of the area exposed to the feeding pressure from pipe 25, so that the piston 11 moves to the left, expelling the oil from compartment 14, and feeding the carriage 7, with its saw 6, toward the work piece 1. The oil from compartment 14 is returned to the pipe 2l.

The deliveries of the principal pump 17 and the feed pump 22 are so proportioned that the principal pump 17 delivers more liquid than can be receivedA by the feed pump 22 so that the oil delivered by the principalpump is backed up in the pipe 21. The pressure of the backed-up oil to which is added the pressure of the oil discharged from the chamber 14 by the advancing piston 11, is transmitted to the tubular valve 29 in the casing 28 by the pipe 27 and opens the valve when the pressure on the valve overcomes the reaction of the spring 37. The excess oil is returned to the reservoir 16 through the holes 30 in the valve 29 and the return pipe 39. The pressure at which the valve 29 opens, and consequently the delivery pressure of the principal pump 17, is a function of the pressure of spring 32 whose initial tension, as mentioned, is regulated by turning the plug 34, but it is also a function of the pressure on the plunger 35. During the idle movement of the carriage 7, the flange 36 of plunger 35 bears on the inner end of the plug 34, but when the saw 6 begins to cut, the resistance increases as the saw penetrates into the work piece 1, tending to reduce the velocity of the feeding movement. The delivery of the feed pump 22, as regulated,l is constant, so that, if the movement of the piston 1l toward the rear compartment 14 is retarded by the resistance of the work piece, pressure builds up in the front compartment 15 and this increased pressure is transmitted to the plunger 35 through the branch pipe 38. The plunger is moved inwardly with respect to the chamber 32 and the tension of the spring 37 is increased so that the valve 29 opens only at a correspondingly higher delivery pressure of the principal pump 17. The higher delivery pressure of the principal pump is transmitted to the rear compartment 14 through pipe 26. If the diameter of plunger 35 is equal to the diameter of the valve body 31, the

-valve 42 opens against the pressure of its spring 43'. In this manner, damage is prevented if, for instance, the carriage 7' abuts against the check which defines vits forward movement.

The oil which escapes through the safety valve 42 is returned to the reservoir 16 through pipe 40, chamber 32 and pipe 39.

When the lever 24 is moved into the neutral position 1I, the feeding movement is arrested and the plunger 35 returns into its initial position, and when the lever 24 is moved into the return position III the bore 49 in the valve 46 connects the pipes 44 and 50. The delivery pipe 25 of the feed pump 22 now becomes its suction pipe, and is ppen to the reservoir 16 through pipe 50, bore 49,

pipes 44 and 40, chamber 32 and pipe 39, so that the oil, which is not drawn into the reversed feed pump is returned by the reservoir 16. The front compartment 15- is emptied rapidly while on the other hand the reversed feed pump 22 now cooperates with the principal pump 17 for delivering oil to the rear compartment 14, eecting rapid return of the piston 11 and the carriage 7.

By suitably adjusting the initial tension of the spring 37 it is possible to eliminate slip in the feed or to purposely bring about a definite amount of slip for reducing the feed with increased resistance.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

In the claims aflixed to this specification no selection of any particular modification of the invention is intended to' the exclusion of other modifications thereof and the right to subsequently make claim to any modification not covered by these claims is expressly reserved.

1. In a machine tool, a carriage for supporting a tool, a fixed cylinder, a piston mounted to reciprocate in said cylinder and operatively connected to said tool-supporting means, a principal pump for supplying fluid under pressure to that face of said piston which effects the return of said carriage, a feed pump whose suction side is connected to the delivery side of said principal pump and whose delivery side is connected to that face of said lpiston which effects the feeding movement of said carriage, a valve casing connected to the delivery side of said principal vpump and to the suction side of said feed pump and having a discharge opening, a, valve in said casing adapted to 'connect the suction side of said feed pump and the delivery side of said principal pump to said discharge opening, a spring for loading said valve, and means controlled in conformity with the resistance to the feed for varying the tension of said spring.

2. In a machine tool, a carriage for supporting a tool, a fixed cylinder, a piston mounted to reciprocate in said cylinder and operatively connected to said tool-supporting means, a principal pump for supplying fluid under vpressure to that face of said piston which effects the return of said carriage, a feed pump whose suction side is connected to the delivery side of said principal pump and whose delivery side is connected to that face of said piston which effects the feeding movement of said carriage, a valve casing connected to the delivery side of said principal pump and 'to the suction side of said feed pump and having a discharge opening, a. valve in said casing adapted to connect the suction side of said feed pump and the delivery side of said principal pump to said discharge opening, a spring for loading said valve, one end of said spring bearing on said valve, a cylinder, a plunger in said cylinder on which bears the other end of said spring, and a pipe connecting said cylinder to the delivery side of said feed pump.

3. In a machine tool', a carriage for supporting a tool, a xed cylinder, a piston mounted to reciprocate in said cylinder and operatively connected to said tool-supporting means, a principal pump, a feed pipe extending from the deliveryside of said principal pump to opposite faces of said piston, a feed pump in said feed pipe which 'pump is adapted to be regulated and adapted to be reversed, whose suction side is connected to the delivery side of said principal pump and whose delivery side (the suction side of the reversed feed pump) is connected to that face of said piston which effects the feeding movement of said carriage through said feed pipe, a bypass connecting the delivery side of said principal pump to the opposite face of said piston, and a valve operatively connected to the means for reversing said feed pump for connecting the delivery side of said feed pump (the suction side of the reversed feed pump) to a discharge pipe in the reversed position of said feed pump.

ERNST HELLER. 

